Mechanical,hygroscopic, and thermal properties of ultrathin polymeric substrates for magnetic tapes

Mechanical, hygroscopic, and thermal properties of improved ultrathin polymeric films for magnetic tapes are presented. These films include poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and aromatic polyamide (ARAMID). PET films are currently the most commonly used polymeric substrate material for magnetic tapes, followed by PEN and ARAMID. The thickness of the films ranges from 6.2 to 4.8 μm. Tensile tests were run to obtain the Young's modulus, F5 value, strain at yield, breaking strength, and strain at break. The storage modulus, E′, and the loss tangent, tan δ, were measured using a dynamic mechanical analyzer (DMA) at temperature ranges of ?50 to 150°C (for PET) and ?50 to 210°C (for PEN and ARAMID) and at a frequency range of 0.016–28 Hz. Frequency–temperature superposition was used to predict the dynamic mechanical behavior of the films over a 28‐decade frequency range. Short‐term longitudinal creep behavior of the films during 10, 30, 60, and 300 s, 7 MPa, were measured at 25 and 55°C. Long‐term longitudinal creep measurements were performed at 25, 40, and 55°C for 100 h. The Poisson's ratio and 50‐h long‐term lateral creep were measured at 25°C/15% RH, 25°C/50% RH, 25°C/80% RH, and 40°C/50% RH. The in‐plane coefficient of hygroscopic expansion (CHE) at 25°C/20–80% RH and the coefficient of thermal expansion (CTE) at 30–70°C were measured for all the samples. The properties for all films are summarized. The relationship between the polymeric structure and the mechanical and physical properties are discussed, based on the molecular structure, crystallinity, and molecular orientation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3052–3080, 2003     

Toughening effect of CPE on ASA/SAN binary blends at different temperatures

The effect of chlorinated polyethylene (CPE) on the impact toughness of acrylonitrile–styrene–acrylic (ASA) terpolymer/styrene–acrylonitrile copolymer (SAN) binary blends (25/75, w/w) was systematically investigated at three different temperatures (?30 °C, 0 °C, and 23 °C). With the addition of 60 phr CPE, the impact strength increased by 11 times at 23 °C and 10 times at 0 °C. However, the toughening effect was not obvious when the testing temperature was ?30 °C. Since the glass‐transition temperature (T_g) of CPE was about ?18.3 °C as measured with dynamic mechanical analysis tests, the polymeric chains of CPE have been “frozen out” at ?30 °C. As a result, CPE evidently cannot improve the toughness of the blend system. The morphology of impact‐fractured surfaces observed by scanning electron microscopy also confirmed the effect of CPE on the impact toughness of ASA/SAN binary blends. The heat distortion temperature remained almost unchanged, indicating that the improvement in toughness did not sacrifice heat resistance. Furthermore, other mechanical properties were evaluated, and the possible interactions among components of the blends were also analyzed by Fourier transform infrared spectra. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43353.     

Effect of service temperature on structure and mechanical properties of polyamide 6 & 66 tyre cords

The effect of service temperature on chemical structure and mechanical properties of polyamide 6 & 66 tyre cords was studied over the broad range of 50–200 °C and for a period of 16 h. The heat treatment of cords at below 100 °C and above 120 °C was found to reduce their tensile properties considerably. The changes in properties above 120 °C were caused by increase in width of the molecular weight distribution curve as ascertained by gel permeation chromatography (GPC) studies and increase in irregularity of the polymeric chains as ascertained by birefringence studies; this appears to be due to the fact that, by raising the temperature, both chain folding and chain scission occur. Since there was deformation of the amorphous regions as ascertained by FTIR spectroscopy and birefringence studies, the changes in properties below 100 °C were attributed mainly to the effectiveness of thermal oxidation and annealing in the amorphous phase. In other words, the degree of crystallinity increased, the tyre cord became brittle, and breaking load and elongation at break were decreased. The lower reduction of tensile properties at an intermediate temperatures of 100–120 °C was caused by the lower polydispersity and irregularity in the polymeric chains, in comparison with higher temperatures and less crystallinity than lower temperature treatments.     

Gas transport properties of polycarbonate–polyurethane membrance

Polyurethanes (PU) were prepared using polymeric diols, containing polar groups, as ? O? C(O)? O? (carbonate) groups, carbonate and ether (? O? ) groups, or carbonate and ester groups [? C(O)? O? ]. PUs were prepared by the prepolymer two-step technique using ethyl acetate (EA) as the solvent; the diol was reacted at about +80°C with TDI (ratio 1:2) to give the prepolymer terminated with NCO, which was then cross-linked with triisopropanolamine (TIPA). The membranes were prepared using a Gardner knife and were characterized by differential thermal analysis (DSC). Most of the polymers prepared from low and medium molecular weight diols were amorphous and elastomeric at the temperature of gas transport measurement (35°C). The permeabilities (P) and the diffusion coefficients (D) of different gases (O₂, N₂, CO₂, CH₄, CO) were measured by a modified Lyssy apparatus, the solubility coefficient (S) was also calculated. The water-vapor transport properties D and S were measured according to ASTM. Diffusivity data follow the Fujita model and the solubility coefficients the regular solution theory, as developed by Prausnitz and Shair. © 1993 John Wiley & Sons, Inc.     

Side‐chain effects on the morphology and properties of fluorene‐based alternating copolymers

Soluble fluorene‐based alternating copolymers containing benzene as the comonomer were synthesized and characterized, in which three different side chains (hydrogen atom, linear octyloxy and bulky benzyloxy groups) were attached to the phenylene ring. The effect of the side chains with different steric hindrances on the photophysical, thermal and electrochemical properties as well as the morphology were investigated. Moreover, the chain conformation and spectroscopic properties in dilute solution were studied to understand the solvent effect. Aliphatic and aromatic solvents were demonstrated to have different influences on the spectra of the polymers owing to various interaction mechanisms in the excited states. Also, a significant decrease of up to 80 °C in the thermal degradation temperature was observed as a result of the introduction of large benzyloxy units. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the polymers were estimated to be ? 5.76 to ? 5.82 eV and ? 2.19 to ? 2.27 eV, respectively, from cyclic voltammetry measurements. In addition, the electronic structures of the polymers were described via quantum chemical calculations. Copyright © 2007 Society of Chemical Industry     

Structure and properties of tailor‐made poly(ethyl acrylate)/clay nanocomposites prepared by in situ atom transfer radical polymerization

An in‐depth study was carried out on the structure and properties of a series of poly(ethyl acrylate)/clay nanocomposites prepared by in situ atom transfer radical polymerization (PNCIs) with well‐defined molecular weights and narrow molecular weight distributions. Wide‐angle X‐ray diffraction and transmission electron microscopy studies revealed an exfoliated clay morphology, whereas conventional solution blending generated an intercalated structure. The storage moduli of the PNCIs showed a moderate increase over that of the neat polymer [poly(ethyl acrylate)]. The sample containing 4 wt % clay (PNCI4, where the number following PNCI indicates the weight percentage of clay) exhibited the highest improvement (31.9% at 25°C). In PNCIs, the β‐transition temperature showed a remarkable decrease (by 175% in PNCI4) along with a shift toward higher temperatures. This indicated the probability of the anchoring of the ? OH group of the clay layers to the >C?O group of the pendant acrylate moiety, which was also confirmed by Fourier transform infrared analysis. Rheological measurements indicated a significant increase in the shear viscosity [by 9% in PNCI2, 15% in PNCI4, and 6% in the poly(ethyl acrylate)/clay nanocomposite with 2 wt % clay prepared by solution blending]. The PNCIs registered enhanced thermal stability, as indicated by the shift in the peak maximum temperature (388 and 392°C for the neat polymer and PNCI4, respectively) and a decrease in the rate of degradation (by 3.5% in PNCI2, 10.2% in PNCI4, and 49.3% in PNCI6). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A new class of thermoplastic elastomers based on polypivalolactone graft systems

Ring-opening graft polymerization of pivalolactone, initiated by carboxylate anion which is randomly located on suitable polymeric substrates, affords high quality thermoplastic elastomers. When processed from the melt, poly(privalolactone) segments readily crystallize into discontinuous domains which serve as reinforcing network tiepoints and melt at 120–225°C according to the average degree of polymerization (P?_n = 4–90) of the graft segments. Transmission electron microscopy shows domain size to be 5–100 nm. Poly([ethylene-co-propylene-co-1,4-hexadiene]-g-pivalolactone) (from carboxylated base polymer) and poly([ethyl acrylate]-g-pivalolactone) were evaluated in detail and have physical properties similar to conventionally cured and reinforced base polymers. The effects of structural variables on morphology and properties are discussed.     

Transitions of polytetrafluoroethylene at about 90 and 130°C. studied by x-ray diffraction and infrared spectra

By means of x-ray diffraction, the lattice spacing of the (100) plane for molded polytetrafluoroethylene was measured at different temperatures from 25 to 190°C. In the crystalline region, the linear expansion coefficient, in the direction perpendicular to the molecular chain axis, was obtained as 1.1 × 10^?4°C.^?1 below 60°C., as 1.2 × 10^?4°C.^?1 above 90°C., and as a minimum value of some 0.2 × 10^?4°C.^?1 at about 80°C. As the linear expansion coefficient of the crystalline region in bulk was observed as some 0.6 × 10^?4°C.^?1, the expansion coefficient in the direction of molecular chain axis must be negative except in the transition region near 80°C. The variation of molecular chain axis separation with temperature showed an irregularity at about 80°C. but none near 130°C. in the crystalline region. Infrared absorbance of film samples of PTFE was measured at different temperatures of 25 to 150°C. range for 518, 627, and 639 cm.^?1 bands. On absorbance–temperature curves for those b?ands, irregularities were observed near 30, 50, 90, and 130°C. Particularly with 518 cm.^?1 band, a more crystalline sample gave more distinct irregularities near 50 and 90°C. than a less crystalline sample. The change at about 90°C. in infrared spectra may correspond to that obtained by x-ray measurements near 80°C., which was thought to occur in the crystalline region. The results obtained by x-ray and infrared measurements support the previous results by thermal, rheological, and dielectric methods: there exist first-order transitions in the crystalline region at about 90°C. and second-order transitions in the amorphous region at about 130°C.     

Design and synthesis of polymeric dispersant for water-borne paint by atom transfer radical polymerization

A series of chains of triblock amphiphilic copolymers were synthesized by atom transfer radical polymerization (ATRP) techniques and post modified to polymeric dispersant for waterborne paint. Poly(butyl acrylate (BA))-b-poly(hydroxy ethyl methacrylate (HEMA))-b-poly(methyl methacrylate (MMA)) triblock copolymers having predetermined molecular weights were synthesized by ATRP using CuBr, 2-bromoisobutyrate, and pentamethyldiethylenetriamine as a catalytic system in dioxane at 80 °C. The copolymers were further reacted with cyclic chlorophosphate and triethyl amine to form dispersible modified poly(BA-HEMA-MMA). The synthesized copolymers were structurally evaluated by Fourier transform infrared, ¹H NMR, ³¹P NMR, gel permeation chromatography (GPC), energy dispersive X-ray spectroscopy, and their hydroxyl equivalent, respectively. The surface activity of modified copolymers as dispersing additives was investigated by the surface tension analysis and wetting ability test. The ability of additives to function as wetting and dispersing agents was evaluated by analyzing their mechanical, optical, chemical, and rheological properties of water-based paints at different pigment volume concentrations. The effects of the chain length of copolymers on dispersibility and optical properties were studied. The optical properties of paints suggested that the dispersibility of modified poly (BA)-b-poly (HEMA)-b-poly (MMA) (MPBHM) increased with an increase in the molecular weight of the copolymer.     

Chemical reactions in crosslinking of copolymers of ethylene and vinyltrimethoxy silane

The crosslinking reactions of a new type of polyethylene, an ethylene vinyltrimethoxy silane (EVS) copolymer, when reacted with water has been studied. Samples of EVS were treated in water at 90°C. The kinetics of the crosslinking was followed by measuring the gel content and by determination of the content of different structures (? Si? OCH₃,? Si? OH, and ? Si? O? Si? ) using FT-IR. The observations show that a maximum gel content of 70-75% is obtained after 25 h treatment in water at 90°C. On the other hand, the absorption index for the crosslinks, ? Si? O? Si? , continues to increase until about 100 h, i.e., more crosslinks seem to be formed without a simultaneous increase in gel content. Mechanical measurements showed decreased elongation at break even after very long treatments. Thermo-oxidative degradation is, however, also responsible for the change in mechanical properties. For properly stabilized samples, the decrease in elongation leveled off after about 100 h of treatment. This indicates that the crosslinks formed after 25 h mainly should be within the already existing gel. The observed synergistic effect of crosslinking and thermo-oxidative degradation emphasizes the importance of a proper stabilizing system.     

Effect of temperature on the joint strength of a silyl-modified polymer-based adhesive

Temperature is a very important factor that must be fully considered in the study on the adhesive joint strength. In this paper, a silyl-modified polymer-based adhesive ISR 70-08 which is widely used in engineering was studied. Dog-bone specimens were fabricated and tested at ?40°C, room temperature (RT), and 90°C. Results show a decrease in the main mechanical properties with increasing temperature. Butt joints (BJs), single-lap joints (SLJs), and Scarf joints (SJs) were fabricated and tested at different temperatures. A quadratic polynomial expression was an ideal choice to express the joint strength as a function of temperature which was obtained using the least-squares method. Temperature combinations of ?40°C, 0°C, and 90°C were obtained to study the effect of temperature on the joint strength more easily for this adhesive. A three-dimensional surface, consisting of temperature, adhesive angle, and joint strength was presented to facilitate the application of bonding structures in engineering     

Temperature and microstructure dependence of the Rheo-optical properties of polybutadienes

The present investigation covers the isothermal stress–strain–birefringence behavior of various polybutadienes between ?30°C and 110°C. Birefringence measurements were also made under constant stress as a function of temperature in the low temperature region between ?30°C and ?120°C. The polybutadienes studied were two high cis-1,4 (prepared by different catalysts), a linear medium cis, and an emulsion polybutadiene. At temperatures at which the photoelasticity theory could be applied, the segmental polarizability anisotropy, its temperature dependence, and other parameters associated with an elastic polymeric network were determined. The influence of the degree of crosslinking was examined. At the low temperatures, microstructure was shown to have a pronounced effect on the photoelastic properties, the crystallization phenomena, and the glass–rubber transitions.     

Determination of Chemical and Mechanical Properties of Double Base Propellants during Aging

Thermal and mechanical stability of rocket and gun propellants are very important properties with regard to safety during storage and handling and to the interior ballistics behavior during combustion. However, our knowledge of how these properties are connected is poor. In order to better understand the aging behavior of double base propellants, the following properties were measured between 60 °C and 90 °C: the depletion of the stabilizers, the degradation of the molecular weights of nitrocellulose and the decrease of the mechanical properties (tensile strength and strain at break). The evaluation of the kinetic parameters of the different aging processes mentioned has shown that stabilizer depletion, molecular weight degradation of nitrocellulose and decrease of mechanical properties must be closely connected.     

Warpage of carbon–epoxy composite channels

Abstract

Finite element models have been developed of the warpage occurring during the cure of unidirectional carbon fibre-epoxy resin channels. These were based on equivalent experimental channels that were formed on a male mould, with the distortions determined separately after cure and post-cure. To quantify the warpage, the decrease in enclosed angle, or spring forward, of the two corners of the U-shaped cross-sections were calculated; values were determined using displacements from both the finite element predictions and measurements of the experimental channels. The experimental channels were fabricated so that several different factors affecting the distortions could be investigated. These included: fibre orientation; cured or post-cured state; conditions of post-cure; fillet radius of the channel corners; and channel thickness, width and depth. Results across the different channels showed predictions of 1° spring forward where the fibres followed the cross-section profile (0° channels), which were fairly accurate, at 75-85% of the experimental values. However, for the channels that had the fibres aligned parallel to the channel length (90° channels), negligible values were predicted, which were considerably lower in magnitude than the experimental values of 0° to-5° (spring back). Subsequent inhomogeneous models and optical microscopy work indicated that the unpredicted spring back in the more flexible 90° channels was caused by a thin (<0·1 mm) resin layer on the outer surface of all the channels. The small underprediction of spring forward in the stiffer 0° channels was attributed to unmodelled cure shrinkage, which was moderated by some reduced spring back due to the presence of a resin layer.     

Preparation of diamine-POSS/Ag hybrid microspheres and its application in epoxy resin

Carbon nanowires having different functionality has been synthesized through the template assisted approach using poly(vinyl alcohol) (PVA) as precursor polymer at 400?°C, 600?°C, 700?°C and 800?°C in the absence of any catalyst. Carbon nanowires with a diameter range of about 90?C120?nm have been obtained. Scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy are been adopted to characterize the morphology, thermal properties and chemical configuration of the synthesized samples. Raman spectroscopy indicates carbonization of the samples upto 600?°C. Above that carbon-cluster formation is observed at 700?°C and 800?°C. SEM images show the formation of nanowires in alumite template by infiltration of PVA into the pores at 400?°C. The nanowires produced are very flexible at about 700?°C, above which the nanowires tended to retain their rigidity due to the formation of graphite clusters / crystallites.     

Melt flow and fiber properties of copolyesters

The effect of modifying monomer [sodium 3,5-di(carbonethoxy)benzene sulfonate] contents range from 1.5 to 4.5 mol % on the melt flow and fiber properties of copolyesters (COPET) dyeable with basic dyes was investigated. An Instron capillary rheometer was used to obtain data over shear rates ranging from 10 to 10⁴ s^?1 at 265, 275, and 285°C. The COPET's flow properties as a function of temperature, inherent viscosity, melting point, and modifying monomer content were determined. The drawn fibers annealed in oil and air at 80, 110, 130, 150, 175, and 200°C were studied by means of measurements of shrinkage ratio, crystallinity, birefringence, long period, sonic rate, and static state flexibility of molecular chain. All these showed that the large side group, ? SO₃Na in COPET molecular chains causes an increase in chain rigidity and melt viscosity, and a decrease in crystallinity and orientation.     

A comparative study on effects of thermal fatigue caused by thermal-oil cycling on tensile properties of single lap composite joints bonded with different kinds of adhesives

In this study, thermal-oil cycling process was applied to adhesively bonded glass fibre reinforced single lap composite joints (SLJs) in order to investigate the effects of thermal fatigue on their tensile properties. Joints were subjected to thermal cycling to achieve the thermal fatigue effect. Initially, separated specimens were heated on a magnetic stirrer from 25°C to 80°C, 25°C to 100°C and 25°C to 120°C and kept at these temperatures for 10 min. Right after that specimens were immersed into heat transfer oil cooled with dry ice at ?10°C for 10 min. and placed back into the magnetic stirrer to reach intended temperatures again. Thus, one cycle is completed. This thermal cycling process was repeated for 1, 10, 20, 30, 40 and 50 times for different groups of specimens. Single lap shear (SLS) tests have been performed for the determination of mechanical properties. As a result of this study, it is found that the load carrying capacities of specimens generally decrease as the thermal cycling count is increased. However, it is observed that specimens subjected to 30 times thermal cycling have the maximum load carrying capacity.     

Order-Disorder Conformation Change of Succinoglycan in Aqueous Sodium Chloride as Studied by Static and Dynamic Light Scattering

Summary Static and dynamic light scattering measurements have been made on a sodium salt sample of succinoglycan in 0.01 M aqueous NaCl at different temperatures between 25 and 75°C where the polysaccharide undergoes a thermally induced change from an ordered (helical) to disordered conformation with raising temperature T. The weight-average molecular weight M _w, the z-average radius of gyration, and the hydrodynamic radius sharply decrease in a relatively narrow T range (around 55°C) in which the specific rotation was previously found to change sigmoidally with T. In particular, the value of M _w (4.55 × 10⁵) in the ordered state at 25°C is twice as large as that (2.27 × 10⁵) in the disordered state at 75°C, giving decisive evidence that the helical structure of the polysaccharide in aqueous NaCl is composed of paired chains. It is concluded that this structure is a double-stranded helix and breaks directly into two disordered chains with increasing T. Received: 6 July 2001 / Accepted: 24 July 2001     

Preparation and sorption studies of β‐cyclodextrin/epichlorohydrin copolymers

β‐Cyclodextrin (β‐CD) copolymer materials were synthesized by reacting different mole ratios (1 : 15, 1 : 25 and 1 : 35) of β‐CD with epichlorohydrin (EP). The products were characterized using N₂ porosimetry, Fourier Transform Infrared spectroscopy, ¹³C CP‐MAS NMR spectroscopy, thermogravimetry analysis, elemental (C and H) analysis, and scanning electron microscopy. The sorption properties in aqueous solution were studied using p‐nitrophenol (PNP) with UV–Vis spectrophotometry. Sorption isotherms were obtained at pH 4.6 and three temperatures (22, 35, and 45°C) and at pH 10.3 at 22°C. The isotherms were analyzed using the BET isotherm model and the sorption parameters provided estimates of the surface area, sorption capacity, and isosteric heats of sorption for each polymeric material. The estimated surface areas are as follows: 58.2, 52.1, and 90.1 m²/g at pH 4.6. At pH 10.3, the estimated surface areas are 44.2, 40.5, and 58.5 m²/g, respectively. The removal efficiency of PNP by the polymeric materials ranged between 4.5 and 58% for the conditions investigated whereas the isosteric heats ranged between ?24.5 and ?13.6 kJ/mol. Removal efficiencies were concluded to strongly depend on the sorption conditions such as pH, temperature, and the relative amounts of sorbent and dye in aqueous solution. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Barrier properties of poly(lactic acid) and its morphological changes induced by aroma compound sorption

The barrier properties of poly(lactic acid) (PLA) play a key role in food packaging applications. For their optimization, the influence of crystallinity on the barrier properties of PLA and the interaction of PLA with the aroma compound ethyl acetate were investigated. PLA film samples with various crystallinities were fabricated by flat die extrusion and thermocompression and compared to PLA Biophan^?. The degree of crystallinity had no effect on the oxygen permeability. However, an increase of crystallinity caused a decrease in ethyl acetate sorption. The sorption isotherm of ethyl acetate obtained using microgravimetry showed a steep increase with increasing aroma activity, a form which is consistent with a plasticization effect. This behaviour was verified using differential scanning calorimetry and dynamic mechanical analysis. Sorption caused a marked decrease in the glass transition temperature well below room temperature to approximately 0 °C. Furthermore, PLA underwent a solvent‐induced crystallization when equilibrated in ethyl acetate atmosphere at an activity of 0.5. The results obtained show the importance of considering possible interactions between polymer and foodstuff during the optimization step of polymeric materials for food packaging applications. Copyright © 2010 Society of Chemical Industry